This invention relates to a process for sealing heating or cooling jackets on industrial processing tanks such as fermentation vessels used in breweries.
Metal processing tanks having heating/or cooling jackets are widely used in chemical, food, pharmaceutical and related industries for batch heating or cooling duties. Typically the cooling jacket will comprise one or more conduits encirculating the tank through which a heating or cooling fluid is circulated. It is common for the jacket to be welded to the tank, sometimes using the outer tank wall as the inner jacket wall. Such welds are also particularly sensitive to the corrosive action of heating or cooling fluids so that they often develop leaks during the surface life of the vessel. Such leaks can cause a number of problems ranging from merely cosmetic to serious damage to surrounding structures and loss of heating or cooling capability.
Heretofore, when such leaks developed it was necessary to attempt to reseal the vessel by rewelding the leaking areas and, if unsuccessful, to rebuild or discard the vessel. Such repairs, even if successful, were extremely expensive, particularly in situations where the tank is lagged with an insulating material and/or the space around the installed vessel is small.
It is known to impregnate porous articles of metal with various materials including acrylic monomer compositions. It is customary in such applications to place the porous articles and the composition in a tank from which the air above the composition is subsequently evacuated. This removes most of the air from the pores of the articles. Normal pressure is restored with the articles submerged in the composition. This drives the composition into the pores. Articles are then removed from the tank and allowed to cure anaerobically or under the influence of heat.
Anaerobic, self-emulsifiable impregnants useful in such applications are described in U.S. Pat. No. 4,165,400 to DeMarco. It is also known to use such compositions to seal automobile engine blocks by injecting the impregnant into interior cavities of the block under pressure.
In U.S. Pat. No. 4,416,921, to Dunn et al., the disclosure of which is incorporated herein by reference, there are described metal insensitive heat curing impregnant compositions comprising: (a) an azonitrile; (b) a polymerizable acrylic compound; (c) a sterically-hindered substituted phenol stabilizer; and (d) a metal ion chelator. Such compositions can be easily cured at temperatures in the range of 75.degree.-90.degree. C.
In U.S. Pat. No. 4,147,821 to Young, there are described other acrylic impregnants which may be heat cured at temperatures below 100.degree. C. It is also known to use styrene based polyester monomer impregnants which are heat cured at temperatures of 120.degree.-150.degree. C.